1. Field of the Invention
A method of determining proximity of a user having a first electronic device to a second electronic device for allowing the user access to the second device.
2. Description of the Related Art
Computer and network security systems frequently include a first electronic device carried by a user, such as token, badge, or card, and a second electronic device, such as a computer, PDA, laptop, or printer. These devices, in order to make the system more reliable, communicate with frequency hopped spread spectrum signals. The second electronic device partitions data into a plurality of data blocks and spreads the transmission of the data blocks over a plurality of frequency channels. Each of the plurality of data blocks is modulated into a distinct and separate signal. The second electronic device transmits the signal at the radio frequency channel for a predetermined time, or dwell time. Sometimes, a portion of the dwell time contains frequency hop information about the next frequency channel to which the second electronic device will be transmitting on. The second electronic device selects the radio frequency channels in a predetermined pseudo-random pattern. By transmitting the data in blocks and at random radio frequency channels, there is little chance that any unintended recipients will intercept the data, therefore creating a secure transmission. Other devices are required to learn the hopping pattern by tracking the hops of the transmission and synchronizing during each hop. Both devices must then spend an undetermined amount of time attempting to synchronize with one another.
These related art systems also include measuring a signal strength and comparing the measured signal strength to a predetermined threshold. One such reference is U.S. Pat. No. 5,821,854 to Dorinski et al. The ""854 Patent to Dorinski et al. discloses a computer and a token carried by a user. The computer and the token each send and receive radio frequency (RF) signals. The computer measures the signal strength of the RF signal emitted by the token and enables the computer in response to the RF signal being above the predetermined threshold. However, the ""854 Patent does not measures multiple signal strengths at different frequencies to determine an overall signal strength to compare to the threshold.
Another related art system is U.S. Pat. No. 5,499,199 to Demas et al. The ""199 Patent to Demas et al. discloses a system for measuring a distance between a base unit and a remote unit. The remote unit transmits a first RF signal to the base unit and the base transmits a second RF signal to the remote unit upon detection of the first RF signal. The remote unit measures a time interval between transmission of the first and receipt of the second RF signal. The ""199 Patent improves the accuracy of the distance by averaging additional time measurements together. However, the system does not measure multiple RF signals at different frequencies.
The related art systems are characterized by one or more inadequacies. The related art systems enable the device when the user may no longer be in proximity to the device thereby allowing for increased information theft. Also, the related art systems do not make accurate RF signal strength measurements when utilizing frequency hopping spread spectrum because of the short transmission periods of the signal.
The subject invention provides a method of determining proximity of a user having a first electronic device to a second electronic device for allowing the user access to the second electronic device. The method includes the steps of transmitting data in a plurality of signals at different frequencies to establish communication between the first electronic device and the second electronic device, detecting the plurality of signals at the different frequencies with the first electronic device, and measuring a signal strength for each of a predetermined number of the detected plurality of signals at the different frequencies. The method characterized by determining an overall signal strength from the predetermined number of measured signal strengths and comparing the overall signal strength to a predetermined threshold for enabling the second electronic device in response to the overall signal strength being above the predetermined threshold.
Accordingly, the subject invention overcomes the inadequacies of the related art systems. The subject invention prevents access to unauthorized users by improving the accuracy of the overall measured signal strength, specifically when communicating via frequency hopping spread spectrum signals. Also, the subject invention determines the overall signal strength to disable the device in response to the user leaving the proximity of the device and thereby preventing information theft.